1. Technical Field
The present invention relates generally to a method for converting waste material into an inert form and particularly concerns a method for alloying the ionic contaminants contained within a metal processing sludge waste material directly into the chemical structure of an inert glass material.
2. Discussion
Current metal processing techniques often produce waste solutions containing heavy metal and other ionic contaminants which are classified as hazardous wastes and require proper disposal. The types of metal processing sources for these waste solutions include chromium plating baths, copper circuit board manufacturing baths, alloy-brightening solutions, zinc plating solutions, electrolysis nickel-plating processes and lead-tin solder etching of copper circuit boards. A former method of disposal of these waste solutions throughout the metal processing industry involved the introduction of lime (calcium oxide) to the solutions containing the ionic contaminants. The introduction of lime caused an increase in the pH of the liquids and a precipitation of metallic and other hydroxides including the contaminants originally contained within the waste solutions. The resulting metallic hydroxide sludge waste material was then filtered to separate the metallic hydroxide precipitates from the filter liquor. The metallic hydroxides were then dehydrated to the oxide form and disposed of in a landfill which is conventional in the industry.
The disadvantage associated with this method of disposal involves the tendency of rain water or acidic materials coming into contact with the metallic hydroxide precipitates to solubilize the contaminants contained therein. This may cause the leaching of metallic contaminants from the landfill. Burying of metallic hydroxide waste sludge has thus become undesirable. In order to remedy this undesirable result, the use of these metal processes must be discontinued, or the contaminants must be removed from these metal processing waste solutions by the application of current costly stabilization processes. The discontinuation of their use entirely, however, would require a costly revision of the solutions currently used in the metal processing industry.
Alternative methods for stabilizing certain metallic elements for disposal are presently known. For example, it is possible to recover chromium from a waste solution by electroplating chromium from solution onto a stainless steel cathode. It is also currently possible to add a chelating agent, such as citric acid, to a waste solution containing iron to chelate the iron, after which the chelate complex is rendered inert and can be disposed of without harming the ground water supply. These methods, however, are both costly and time-consuming. Such stabilization processes also do not always ensure a safe containment of the metallic waste products, as the contaminants may still be susceptible to ground water and other solvent solubility.
The need therefore exists for a new method for stabilizing metallic elements from metal processing waste solutions into a chemically acceptable condition for disposal.